The present invention relates to the construction of energy systems, and more specifically relates to high performance energy or power systems that employ chemical converters. The chemical converters may be electrochemical devices such as fuel cells or electrolyzers, or chemical devices such as reformers.
Electrochemical devices, such as fuel cells, convert chemical energy derived from fuel stocks directly into electrical energy. The key components in an electrochemical device are a series of electrolyte units having electrodes disposed over its surfaces, and a series of interconnectors disposed between the electrolyte units to provide serial electrical connections. The electrolyte units have fuel and oxidizer electrodes attached to opposite sides. Each electrolyte unit is an ionic conductor having low ionic resistance thereby allowing the transport of an ionic species from one electrode-electrolyte interface to the opposite electrode-electrolyte interface under the operating conditions of the converter. Various electrolytes can be used in such converters. For example, zirconia stabilized with such compounds as magnesia, calcia or yttria can satisfy these requirements when operating at an elevated temperature (typically around 1000° C.). The electrolyte material utilizes oxygen ions to carry electrical current. The electrolyte should not be conductive to electrons which can cause a short-circuit of the converter. On the other hand, the interconnector must be a good electronic conductor. The interaction of the reacting gas, electrode and electrolyte occurs at the electrode-electrolyte interface, which requires that the electrodes be sufficiently porous to admit the reacting gas species and to permit exit of product species. Electricity is generated through electrodes and the electrolyte by an electrochemical reaction that is triggered when a fuel, e.g., hydrogen, is introduced over the fuel electrode and an oxidant, e.g., air, is introduced over the oxidizer electrode. The electrochemical devices can also have a tubular or planar configuration.
Alternatively, the electrochemical devices can be operated in an electrolyzer mode, in which the electrochemical devices consume electricity and input reactants and produces fuel.
When an electrochemical device performs fuel-to-electricity conversion in a fuel cell mode, waste energy is generated and should be properly processed to maintain the proper operating temperature of the electrochemical device and to boost the overall efficiency of the power system. Conversely, when the device performs electricity-to-fuel conversion in the electrolyzer mode, the electrolyte must be provided with heat to maintain its reaction
Furthermore, the device when used to reform fuel, requires the interchange of thermal energy. Thus thermal management of the electrochemical device for proper operation and efficiency is important.
Environmental and political concerns associated with traditional combustion-based energy systems, such as coal or oil fired electrical generation plants, are elevating interest in alternative energy systems, such as energy systems employing electrochemical devices. Nevertheless electrochemical devices have not found widespread use, despite significant advantages over conventional energy systems. For example, compared to traditional energy systems, electrochemical devices such as fuel cells are relatively efficient and do not produce pollutants. Accordingly, electrochemical energy systems can benefit from additional development to maximize their advantages over traditional energy systems and increase the likelihood of their widespread use.
Conventional energy devices, such as gas turbine power systems, exist and are known. Prior gas turbine power systems include a compressor, a combustor, and a mechanical turbine, typically connected in-line, e.g., connected along the same axis. In a conventional gas turbine, air enters the compressor and exits at a desirable elevated pressure. This high-pressure air stream enters the combustor, where it reacts with fuel, and is heated to a selected elevated temperature. This heated gas stream then enters the gas turbine and expands adiabatically, thereby performing work. One drawback of gas turbines of this general type is that the turbine typically operates at relatively low system efficiencies, for example, around 25%, with systems of megawatt capacity.
Thus, there exists a need in the art for high performance energy systems. In particular, an improved power system employing an electrochemical device and a conventional energy device that employs structure to increase operational efficiency while concomitantly enhancing system safety would represent a major improvement in the industry.